1. Field of the Invention
This invention relates to integrated circuit manufacture and, in particular, manufacture of integrated circuits having a region of titanium nitride.
2. Art Background
The use of titanium nitride has been widely suggested for various applications in integrated circuit manufacture. Indeed, such use has become even more significant as design rules become smaller. (The device design role is the smallest lateral dimension for all features within the device circuit.) For example, in the manufacture of integrated circuits, titanium nitride is employed for electrical interconnections. Additionally, in integrated circuit manufacture titanium nitride is used in some approaches to form electrical contacts at junctions such as the source, drain and gain of field effect transistors.
The latter application is particularly demanding. For these contacts desirable electrical properties include a junction contact resistance less than 10 ohms/.mu.m.sup.2 and a junction leakage current less than 10.sup.-8 amp s/cm.sup.2. Complexities inherent in strict design rules make satisfaction of these requirements significantly more difficult. For example, since the source and drain junctions are typically no deeper than 0.25 .mu.m at submicrons design rules, any undesirable chemical reaction with the junction induced by the fabrication process quickly destroys it. Additionally, electrical contact is made through an opening in an overlying dielectric to the underlying junction region, e.g., drain or source junction region. Typically, as a consequence of strict design rules, this opening (generally referred to as a window or via) has a high aspect ratio, i.e., greater than 1.0. (Aspect ratio is defined as the thickness of the dielectric at the junction divided by the effective diameter of the via/window at the junction, i.e., the diameter of a circle having the same area as the via/window at the junction.) To contact the junction through a high aspect ratio opening requires deposition of a conductive material that conforms to or fills the opening so that the conducting cross-section in the via/window is adequate to maintain an acceptably low current density and contact resistance. Thus, in summary, to ensure a suitable contact, undesirable chemical reaction with the junction should be avoided while a coating that conforms to or fills the via/window should be produced.
One promising approach for satisfying the difficulties associated with strict design rules involves the blanket deposition of titanium nitride to cover the surface of the silicon dioxide and to form a region at the bottom of the via/window. The titanium nitride provides an adhesion layer for subsequent deposition of, for example, tungsten on the surface overlying the silicon dioxide. Additionally, this region aids in the formation of the contact to, for example, the source and drain by initiating the interface between the contact and such source or drain. Thus, in one embodiment, titanium nitride is first deposited to coat the surface of the silicon dioxide and bottom of the vias/windows through the silicon dioxide. Subsequently, tungsten is deposited by an expedient such as chemical vapor deposition from tungsten hexafluoride and a reducing agent such as hydrogen. (See Lifshitz 3-7, U.S. Patent application Ser. No. 226,917, dated Aug. 1, 1988, which is hereby incorporated by reference.)
Various methods have been developed for the deposition of titanium nitride. For example, titanium nitride is sputtered by processes such as described in P. R. Fournier, U.S. Pat. No. 3,798,145, or H. von Seefeld, et al., IEEE Transactions Electron Devices, 27,873 (1980). However, generally it is believed that sputtering processes do not produce a suitable conformal coating for subsequent processing. That is, the coating such as shown in FIG. 1 has extremely thin comers that typically, in subsequent metallization, produce contact failure at the bottom comers of the via/window. Additionally such configuration promotes voids in the metal filling the via or window formed during the subsequent deposition process.
Plasma deposition processes such as described by D. H. Jang, et al. Thin Solid Films, 169, No. 2, pp. 57-68 (1989), generally are performed at rf plasma frequencies and typically result in a deposited titanium and nitrogen containing material that includes bound chlorine. This bound chlorine is undesirable since it affords the potential for serious corrosion of metal regions of the device. Similarly the formation of titanium nitride by chemical vapor deposition (CVD) using gas precursors such as titanium tetrachloride and ammonia also leads to titanium/nitrogen materials containing bound chlorine. Thus, although titanium nitride appears to be of potential significance in the fabrication of devices, it would benefit from an improved process.